I believe that the advice not to make big decisions right away is in regard to the future being so unstable.
I don't think it necessarily means divorce vs reconciliation, but includes making large purchases like a car or a house. You have to take in consideration that your lifestyle may change, and what might seem good for the moment, might not be suitable in a month or year from now. Also, decisions can mean changes, which could likely add more unnecessary stress when you have other things to focus on.
I also want to add, that if someone decides that an A is a deal breaker early on, it doesn't necessarily mean that the decision to divorce is a rash one. Sometimes the writing is clearly on the wall, other times, its not as easy to read (or we don't want to read it)